In general, it is well known that organic base substances are affected by light, for example organic dyes often fade or discolor. In the fields of formation of inks, dyeing of fibers and color photography, various studies have been performed toward inhibiting fading or discoloration of organic dyes, or that is, to improve the light-fastness or light-resistance of organic dyes. The present invention can be used extremely advantageously for the purpose of improving the light-fastness of the above-mentioned organic base substances.
The term "organic base substances or base compounds" as used herein includes substances which can visually be seen as colored or colorless by human eyes under irradiation of sun light; therefore, it includes not only substances having an absorption maximum in a visible range but also other substances, for example optical brightening agents or substances having a maximum absorption in an infrared range. In accordance with the present invention, the organic base substances include organic substances which have an absorption maximum in the range of from about 300 nm in an ultraviolet range to about 2000 nm in an infrared range.
The term "dyes or colors" as used herein includes organic substances which can be seen as colored by the naked eye under irradiation of sun light.
The term "light" as used herein means an electromagnetic wave having a wavelength of less than about 2000 nm, and it includes an ultraviolet ray of less than about 400 nm, a visible ray of from about 400 nm to about 700 nm, and a near infrared ray of from about 700 nm to about 2000 nm.
Hitherto, it has been known that such organic base substances, for example dyes or colors, are adversely affected by light, often fading or otherwise deteriorating. There are various reports relating to methods of lowering the color-fading or discoloration or methods of improving the light-fastness of colors and dyes. For instance, U.S. Pat. No. 3,432,300 discloses a method of blending therewith an organic compound, such as indophenol, indoaniline, azo or azomethine dyes, and a phenol type compound having a condensed heterocyclic structure, to thereby to improve the light-fastness of the dyes against light in the visible and ultraviolet ranges.
In general, in the field of silver halide photographic materials, azomethine dyes or indoaniline dyes are formed by the reaction of the oxidation product of an aromatic primary amine developing agent and a coupler, as described in C. E. K. Mees & T. H. James, The Theory of the Photographic Process (published by Macmillan, 1967), Chap. 17, and various means have been known for improving the stability against light of the color images formed from said dyes. For example, as stabilizers there are known the hydroquinone derivatives described in U.S. Pat. Nos. 2,360,290, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801 and 2,816,028, and British Pat. No. 1,363,921; the gallic acid derivatives described in U.S. Pat. Nos. 3,457,079 and 3,069,262, and JP-B-43-13496 (the term "JP-B" as used herein means an "examined Japanese patent publication"); the p-alkoxyphenols described in U.S. Pat. Nos. 2,735,765 and 3,698,909; and the chroman and coumaran derivatives described in U.S. Pat. Nos. 3,432,300, 3,573,050, 3,574,627, 3,764,337, 3,574,626, 3,698,909 and 4,015,990.
However, although these compounds have an anti-fading or discoloration-preventing effect, the effect thereof as an anti-fading or discoloration-preventing agent is not sufficient.
British Pat. No. 1,451,000 mentions a method of improving the light-stability of organic base compounds by the use of azomethine quenchers having an absorption maximum in the range of a deeper color than the absorption maximum of the base compounds. However, since the azomethine quenchers themselves are strongly colored, this is disadvantageous because of having a noticeable influence on the hue of the base substances.
It has also been known from the past that polymer compounds, such as polyolefins, are deteriorated by light. In order to prevent such deterioration, an ultraviolet absorber, such as benzophenone derivatives as well as hindered amines, have heretofore mostly been used. However, although these absorbers were somewhat effective for reducing the deterioration of polymers by light, the effect thereof was not sufficient.
On the other hand, British Pat. No. 869,986, U.S. Pat. No. 4,050,938 and Research Disclosure No. 15162 (1976) disclose a method of stabilization of dyes with metal complexes. O. Cicchetti, Adv. Polymer Sci., 7, 70 (1970}; M. S. Allen & J. F. Mckellar, Chem. Soc. Rev., 4, 533 (1975); D. J. Carlson & D. M. Wiles, J. Macromol. Sci. Rev. Macromol. Chem., C14, 65 (1976); R. B. Walter and J. F. Johnson, J. Polymer Sci., 15, 29 (1980); and N. S. Allen, Chem. Soc. Rev., 15, 373 (1986) mention the use of metal complexes for the prevention of light-deterioration of polymers. However, the discoloration-preventing effect or anti-fading effect itself of these compounds is not so high. In addition, the solubility thereof in organic solvents is not high; and, it is difficult to uniformly disperse them in polymers. Accordingly, it is impossible to add the complexes to polymers or dyes in an amount sufficient to display the discoloration-preventing effect or anti-fading effect thereof. Moreover, since the complexes themselves are noticeably colored, they adversely influence organic base substances, especially on the hue and purity of dyes, when added to base substances in a large amount.